fix(vim): drop problematic diffopt from settings.vim
fix(vim): drop problematic diffopt from settings.vim

Not sure why, but on the Vim version I am currently testing (8.2, as
provided by Apple on Big Sur), this line causes:

    E474: Invalid argument: diffopt+=foldcolumn:0

at boot. As my Vim config is on life-support at this point, I'm just
removing the problematic line.

wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent